What is Block Cipher?
An encryption algorithm that processes data in fixed-size blocks, used as the foundation for most symmetric encryption systems.
Block ciphers encrypt data in chunks (blocks) of a fixed size, typically 128 or 256 bits.
Common Block Ciphers
- AES: 128-bit blocks. The global standard.
- Twofish: 128-bit blocks. AES finalist, still considered secure.
- Serpent: 128-bit blocks. Most conservative AES finalist.
- Blowfish: 64-bit blocks. Aging, replaced by Twofish.
- DES/3DES: 64-bit blocks. Obsolete.
Modes of Operation
Block ciphers need a "mode" to encrypt data larger than one block:
- ECB: Encrypts each block independently. Insecure — reveals patterns.
- CBC: Chains blocks together. Secure but sequential.
- CTR: Turns block cipher into a stream cipher. Parallelizable.
- GCM: CTR + authentication. Recommended for most uses.
Why It Matters
The mode is as important as the cipher. AES-ECB is insecure despite using AES. AES-GCM is excellent. Always check the full algorithm specification, not just the cipher name.
Related Terms
AES
Advanced Encryption Standard is a symmetric encryption algorithm adopted by the U.S. government and used worldwide. It's the gold standard for encrypting sensitive data, used in everything from HTTPS to disk encryption.
Symmetric Encryption
An encryption method where the same secret key is used for both encrypting and decrypting data. While fast and efficient, the challenge lies in securely sharing the key between parties.
Have more questions?
Use our guided flow to get the right next privacy step for Block Cipher.
Open Guided Flow